The entire disclosure of any publication or patent document mentioned herein is incorporated by reference, including U.S. Publications No. 2013/0266033 and 2013/0322825.
Optical fiber transmission systems are employed in data centers to establish communication between devices such as routers, servers, switches and storage devices. The optical fiber transmission system typically utilizes a trunk cable (e.g., tens to hundreds of meters long) that carries many optical fibers (e.g., twelve, twenty-four, forty-eight, etc.). Each end of the trunk cable optically connects to a breakout assembly to transition from MPO-style multifiber trunk connectors to other types of connectors which are then interfaced with patch cords or plugged directly into equipment ports, thereby establishing an optical path between the devices. The breakout assembly is frequently housed in a break-out module.
Data centers are configured with cable assemblies containing multimode optical fibers. Such fibers are used because the light sources in the transceivers in the optical devices are multimode light sources. Also, historically it has been easier to work with multimode fiber than single-mode fiber. Unfortunately, multimode fiber has a smaller bandwidth-distance product due to modal dispersion, which makes it difficult and expensive to extend the reach or to increase the data rate of the optical fiber transmission system.
In addition, the existing multimode fibers are optimized for operation at a nominal wavelength of 850 nm at which multimode fibers have high chromatic dispersion. For longer reach or higher data rate transmission, it is desired to have an operating wavelength of nominally around 1300 nm where the chromatic dispersion is the lowest. For example, many single-mode transceivers, such as LR and LRM transceivers, are designed and operated at a nominal wavelength of 1310 nm. Some of the transceivers operating at a wavelength of about 1300 nm involve CWDM or four wavelengths propagating with the same optical fiber at 10 Gb/s for each wavelength, so that the total data rate for each transceiver is 40 Gb/s.
The wavelengths for each operating channel are nominally 1270 nm, 1290 nm, 1310 nm and 1330 nm. Traditionally they are operated with single-mode fibers, with the exception of an LRM transceiver, which can operate with a single-mode to multimode fiber patch cord with offset splicing so that multimode fiber can also be used. But recently there has been increasing interest in using the single-mode transceiver with multimode fiber in data center for improved interoperability, providing a smooth upgrade path and for easier logistical management, all of which provide economic and financial benefits.
Consequently, it is advantageous to have ways of improving the performance of a multimode optical fiber transmission system without incurring the time, labor and expense of having to replace the multimode fibers.